Known properties of polyarylene sulfide (PAS), e.g., polyphenylene sulfide (PPS) include excellent solvent resistance, chemical resistance, heat resistance, tensile strength, and stiffness, however PAS has a characteristic low elongation at yield and ultimate elongation at break. PAS is often further compounded with glass and mineral for increasing the strength and stiffness. In one embodiment of PAS, PPS is highly rigid and not suitable for forming flexible extruded piping for aggressive fuel or chemical media transport applications without further modification. Among the known impact modifiers potentially suitable for improving the impact strength of PPS, difficulties can be encountered due to relatively high temperatures required to melt-process PPS.
EP 0 435024 discloses use of hydrogenated nitrile rubber for impact modification of PPS, however only moderate improvements are seen. It would be desirable to obtain further improvement in notched Izod impact strength and higher elongation at break.
U.S. Pat. No. 5,270,305 discloses an impact modified polyarylene sulfide comprising 60-99 parts by weight of a polyarylenesulfide, and 40-1 parts by weight of a polyorganosiloxane graft copolymer (B) prepared by grafting a vinyl monomer on a polyorganosiloxane rubber having a degree of swelling in a range of 3-50 measured using toluene as a solvent.
U.S. Pat. No. 4,889,893 discloses a two-component PPS composition that contains an olefinic copolymer containing 60 to 99.5% of an α-olefin and 0.5 to 40% by weight of a glycidyl ester of an α,β-unsaturated carboxylic acid, e.g., ethylene-glycidyl methacrylate. The olefinic nature of the modifier makes it somewhat susceptible to chemical attack, particularly at relatively high continuous use temperatures. At usage levels above wt. 20% in mixture with PPS, ethylene-glycidyl methacrylate modifier, at high temperatures tends to self-associate and causes surface blemishes or imperfections or gels in extrudates. Such blemishes are more visible when the PPS compound is not further modified with fillers and reinforcing fibers.
U.S. Pat. No. 6,889,719 discloses a multilayer pipe for liquid antifreeze transport that has the inner layer made of resin material having a PPS resin that may optionally contain 20 to 40% by weight of a softening material from ethylene-glycidyl methacrylate (EGMA) and ethylene-propylene copolymers. Since the modifiers are polyolefin based, such a composition has limitations for use in fuel transport under processing temperatures of elevated temperatures. Also, the EGMA based elastomer has a tendency to self associate under PPS processing conditions.
The use of elongated metal tubing in oil and gas wells instead of a string of interconnected tubing sections is widespread. Thermoplastic tubing has the potential to reduce cost and weight but is not without its drawbacks. For an elongated tubing to be coiled on a reel it must be relatively thin-walled and of a relatively small diameter for working over wells and convey chemicals transported through the tubing down hole quickly and inexpensively. It would be desirable to obtain the combination of low degree of swelling in chemical media, increased elongation at break and impact strength to allow for the extrusion of tubing which can be spooled and unspooled without damaging the tubing itself. Objects of the invention include providing thermoplastic PAS compositions that when formed into elongated conduits, are capable of carrying corrosive fluids over a long service life without causing corrosion.
A specific object of the invention is to provide PAS compounds having a balance in elongation at break and impact strength, without compromising much of the inherent chemical resistance of PAS and yet provide extruded spoolable tubings therefrom for transporting chemical fluids. The extruded tubings must additionally exhibit a smooth surface. The aforementioned improvements heretofore have not been shown in PAS compounds presently.